1. Field of the Invention
The present invention relates to a wet etching system, and more particularly, to an etchant fume exhaust apparatus installed in the etching system being used in an etching process for the fabrication of a liquid crystal display device, for discharging the etchant in a vapor and liquid state out of the system thereby to prevent the contamination and corrosion of the etching system.
2. Description of the Related Art
With the recent rapid development of the technologies in semiconductor device fabrication industries, improved liquid crystal display (LCD) device products are produced that are thinner and lighter. The CRT (cathode ray tube), being widely used for display devices until now, has advantages in functionality and price, but also has many disadvantages including difficulty in miniaturization and portability.
In contrast, LCD devices have many more advantages than CRTs, especially when it comes to mobile devices. These advantages include the ability to miniaturize the devices, the devices are comparatively lightweight, and have relatively low power consumption. LCD devices have become so common that they are replacing the conventional CRT devices, especially as they overcome the above problems of the CRT. Nowadays, LCD devices are used in almost all information processing systems which need display devices.
In the meantime, one driving principle of the LCD device is the optical anisotropy and the polarization property of its liquid crystal material. Since the liquid crystal material is thin and long in its structure, its molecular alignment direction can be adjusted depending on the electric field applied to a liquid crystal material having a particular orientation and polarization.
Therefore, by arbitrarily adjusting the alignment direction, light can be transmitted or blocked dependent on the alignment direction of the liquid crystal molecules by the optical anisotropy of the liquid crystal material so as to display colors and images.
Typically, the LCD device includes a first substrate (thin film transistor substrate) and a second substrate (color filter substrate), which are separated and arranged to face each other.
One exemplary description of a fabrication process of the first substrate of the LCD device will be as follows.
First, a metal layer is deposited on a transparent glass substrate, and a first mask process is performed to form a gate bus line and a gate electrode by etching. Then, by depositing a gate insulating layer, an amorphous silicon layer, and a doped amorphous silicon layer in sequence, a second mask process is performed to form a channel layer.
Then, a third mask process is performed by depositing a source/drain metal layer on the substrate having the channel layer formed thereon, and then, by etching to form a source/drain electrode and a data bus line. Further, a protection layer to protect device elements is deposited, and a fourth mask process is performed to form contact holes. Then, an ITO transparent metal layer is deposited on the substrate having the protection layer formed thereon, and by etching, a fifth mask process is performed to form a pixel electrode.
As described above, a patterning process is performed by depositing or coating a metal layer and an insulating layer on the transparent glass substrate alternately. In the case of a metal layer, the metal layer is etched by wet etching, and in the case of an insulating layer, dry etching is used by using plasma molecules.
In etching processes, the conditions of pressure and ion molecular concentration of plasma in the etching chamber are controlled dependent on the etched subjects.
Further, a black matrix in a lattice shape is formed on the transparent upper substrate of the color filter substrate. Then, color filter layers of red (R), green (G), blue (B) are formed on the black matrix to complete the color filter substrate.
Further, in the formation of the black matrix, a metal layer such as chrome is formed on the substrate by using vacuum deposition, for example, and a photosensitive resin is formed thereon. Then, patterning is performed by using photolithography and the chrome is subsequently etched.
As such, a wet etching process is included in the fabrication of the thin film transistor substrate and the color filter substrate. Such a wet etching process is classified into PSL (poly spacer LOCOS) or STI (shallow trench isolation) structure of active define process and via round etching process or the like. The etchant used in the wet etching process can be roughly classified into two component group and three component group compounds.
The two component group compound includes HF and deionized water (DIW) in which the HF dissolved in the DIW is dissociated into a small amount of HF2 to etch an oxide layer. The three component group compound is called SBOE (surfactant buffered oxide etchant), and is composed of HF, NH4F, DIW, and negative ion surfactants. In such an SBOE group etchant, all HF in the DIW is dissociated into HF2 by the added NH4F.
In the fabrication process of an LCD device, compounds such as those above are mixed and used as the etchant. The structure of the etchant supply apparatus employed in a typical etching system is illustrated in FIG. 1. FIG. 1 is a schematic representation of an etchant supply apparatus in a typical etching system.
As shown in FIG. 1, an etchant supply apparatus 100 includes a first etchant tank 110a and a second etchant tank 110b, which contain the etchant compound described above. The etchant supply apparatus 100 also includes a pump 150 for supplying the etchant from the first etchant tank 110a and the second etchant tank 110b to a supply pipe 130.
Further, etchant fume exhaust units 120a, 120b are provided in the upper portion of the etchant supply apparatus 100, for discharging a gas state of the etchant out of the etching system. Further, after the etching process is completed, a return line 140 is provided such that the etchant used in the etching process can be returned into the first etchant tank 110a and the second etchant tank 110b. 
Though not shown in the drawing, the etchant supply apparatus 100 further includes a self-circulation unit and a filter unit for filtering the returned etchant and a coolant supply part, for example.
Describing in more detail, the etchant supply apparatus 100 structured as above mixes the etchant compound contained in the first etchant tank 110a and the second etchant tank 110b by the movement of the pump 150, and supplies the mixed etchant to a chamber (not shown) being used for the etching process. Then, when the etching process is performed in the fabrication of a thin film transistor substrate and a color filter substrate of an LCD device, the etchant supply apparatus 100 supplies the mixed etchant to the substrate for which the etching is processed.
After the etching process is done, the etchant used in the etching process passes through the return line 140 of the etchant supply apparatus 100 and comes back into the first etchant tank 110a and the second etchant tank 110b. Further, when another etching process is performed for the substrate, the etchant supply apparatus 100 supplies etchant to the chamber by the movement of the pump 150.
In the etchant supply apparatus 100 of the etching system, the supply of etchant to the chamber, and the return of the etchant from the chamber are all repeatedly performed. During the repetitive supply and return of the etchant described as above, the etchant, being very volatile, becomes gaseous and rises up over the etchant supply apparatus 100. Thus, etchant fume exhaust units 120a, 120b are provided in the upper portion of the etchant supply apparatus 100 for discharging the gas state of etchant out of the system.
FIG. 2 is an exemplary conceptional representation of the structure of the etchant fume exhaust apparatus installed in a conventional etching system.
As shown in FIG. 2, an exhaust hole 200 is provided in the etchant exhaust apparatus. The etchant hole 200 is located in the upper portion of the etchant supply apparatus, and is configured to penetrate the apparatus 100 so that the gas state of etchant, which has risen upward, is discharged out of the apparatus 100 through the exhaust hole 200.
While the gas state of the etchant is being discharged through the exhaust hole 200, the rising etchant often re-liquefies in the exhaust hole 200. This re-liquefied etchant returns back into the apparatus 100 from the exhaust hole 200, and the dripping etchant falls down on the etching system. This causes problems in contamination and corrosion of the etching equipment in the apparatus 100.